Strong anthropogenic control of secondary organic aerosol formation from isoprene in Beijing

Abstract

Abstract. Isoprene-derived secondary organic aerosol (iSOA) is a significant contributor to organic carbon (OC) in some forested regions, such as tropical rainforests and the Southeastern US. However, its contribution to organic aerosol in urban areas that have high levels of anthropogenic pollutants is poorly understood. In this study, we examined the formation of anthropogenically influenced iSOA during summer in Beijing, China. Local isoprene emissions and high levels of anthropogenic pollutants, in particular NOx and particulate SO42-, led to the formation of iSOA under both high- and low-NO oxidation conditions, with significant heterogeneous transformations of isoprene-derived oxidation products to particulate organosulfates (OSs) and nitrooxy-organosulfates (NOSs). Ultra-high-performance liquid chromatography coupled to high-resolution mass spectrometry was combined with a rapid automated data processing technique to quantify 31 proposed iSOA tracers in offline PM2.5 filter extracts. The co-elution of the inorganic ions in the extracts caused matrix effects that impacted two authentic standards differently. The average concentration of iSOA OSs and NOSs was 82.5 ng m−3, which was around 3 times higher than the observed concentrations of their oxygenated precursors (2-methyltetrols and 2-methylglyceric acid). OS formation was dependant on both photochemistry and the sulfate available for reactive uptake, as shown by a strong correlation with the product of ozone (O3) and particulate sulfate (SO42-). A greater proportion of high-NO OS products were observed in Beijing compared with previous studies in less polluted environments. The iSOA-derived OSs and NOSs represented 0.62 % of the oxidized organic aerosol measured by aerosol mass spectrometry on average, but this increased to ∼3 % on certain days. These results indicate for the first time that iSOA formation in urban Beijing is strongly controlled by anthropogenic emissions and results in extensive conversion to OS products from heterogenous reactions.

Organosulfates in atmospheric aerosols in Shanghai, China: seasonal and interannual variability, origin, and formation mechanisms

“…5a, b). A similar result was also found in Beijing that most OS species were (Bryant et al, 2020). In addition, an overall positive correlation was observed between the OS concentration and ALWC (Fig.…”

“…We note that the 2-MT-OS/2-MA-OS ratios observed in summertime Shanghai are smaller than those (17.0-33.8) observed in less polluted environments such as the southeastern United States (Budisulistiorini et al, 2015;Hettiyadura et al, 2019;Riva et al, 2019), but significantly larger than those (0.55-1.57) observed in Beijing Bryant et al, 2020) and the Pearl River Delta (PRD) region of China (He et al, 2018).…”

“…This implies that the Ox level is a driving factor for OS formation in ambient aerosols in Shanghai. Very recently, a similar oxidant effect on OS formation was also observed in urban Beijing (Bryant et al, 2020). Therefore, mitigation of Ox pollution may effectively reduce the production of OS and SOA in Chinese megacities.…”

Low-NO atmospheric oxidation pathways in a polluted megacity

“…Both are tracers for non-NOdriven chemistry. While 2-methyltetrol-OS is formed via the ISOPOO + HO 2 IEPOX pathway (Paulot et al, 2009;Surratt et al, 2010;Lin et al, 2012), 2-MGA-OS (Lin et al, 2013) is formed from the OH-initiated oxidation of MPAN (peroxymethacrylic nitric anhydride) (Kjaergaard et al, 2012;Nguyen et al, 2015a), with further oxidation leading to 2-MGA (Surratt et al, 2010;Chan et al, 2010;Nguyen et al, 2015a). MPAN is a product of the OH-initiated oxidation of MACR in an environment with a high NO 2 /NO ratio.…”

Coupling a gas chromatograph simultaneously to a flame ionization detector and chemical ionization mass spectrometer for isomer-resolved measurements of particle-phase organic compounds

“…Additionally, the use of a GC column, which is selective towards a certain range of volatility and polarity of compounds, which limits the detection of compounds. Conversely, thermal desorption within TAG may fragment larger accretion products to form analytes not present in the original sample (Buchholz et al, 2020;Isaacman-VanWertz et al, 2016;Lopez-Hilfiker et al, 2016b;Stark et al, 2017) or may reverse particle-phase oligomerization reactions (Claflin and Ziemann, 2019). These fragments may not represent the ac- Data in (b) are from ambient atmospheres in a ponderosa pine forest in California measured by two-dimensional GC without derivatization (Worton et al, 2017), southeastern USA by two-dimensional GC with derivatization (Zhang et al, 2018), and combined datasets from SOA formation measured by liquid chromatography (Bryant et al, 2019;Dixon, 2020).…”